The present invention relates to an automatic ice making apparatus for use in a home refrigerator.
In a first example of conventional automatic ice making apparatus, the state of freeze of water is determined by a thermostat mounted on an ice making tray, and the thermostat is used for sensing the temperature and for switching over an electric heater or an ice discharging motor, for example. In such automatic ice making apparatus, the operation temperature of the thermostat is set generally to about minus 10xc2x0 C. When the thermostat is operated at a temperature of about minus 10xc2x0 C., a contact of switch of the thermostat is closed to energize the electric heater mounted on the ice making tray, so that the ice making tray is heated, the surface of ice contacted to the ice making tray is melted, and the ice is removed from the ice making tray.
The ice discharging motor for use in an ice discharging mechanism is energized at the same time of the switching over of the thermostat by the switching function thereof, however, the motor is deenergized when a claw for discharging ice is brought into contact with the ice, and then the motor is energized when the ice is removed from the ice making tray to discharge the ice from the ice making tray. It is a matter of course that the ice discharging motor is of the type to be remained in the deenergized state for a while.
The hysteresis property is applied to the thermostat in order to separate positively the ice from the ice making tray. That is, the switch contact of the thermostat is turned ON at about minus 10xc2x0 C. and turned OFF at about plus 10xc2x0 C. Due to the hysteresis property, when the temperature of the ice making tray is elevated to about plus 10xc2x0 C., the switch contact of the thermostat is turned OFF to deenergize the electric heater.
A cam for operating two limit switches is provided on the ice discharging motor. One of the limit switches serves as to turn ON or OFF an electromagnetic valve for supplying water. The other of the limit switches is connected in parallel with the switch contact of the thermostat, so that the ice descharging motor is rotated continuously even if the switch contact of the thermostat is turned OFF. After the ice has been discharged perfectly, the ice discharging motor is still rotated, and the electromagnetic valve is energized by the cam and the limit switch for a period of time determined by the number of rotation of the motor and the figure of the cam so as to supply water.
Then the ice discharging motor is deenergized and the water supply is stopped. The above is a cycle of the ice making.
In a second example of the conventional automatic ice making apparatus, the state of freeze of water is determined by such a control system that the temperature of an ice making tray is detected by using a thermistor mounted on the ice making tray as a temperature sensor, and an output voltage of the thermistor is compared to a predetermined value and judged by a comprator whether the temperature of the ice making tray is higher or lower than the predetermined temperature. The automatic ice making apparatus of this system is similar basically to the first example of the conventional automatic ice making apparatus except that in the second example of the automatic ice making apparatus a semiconductor switch is used as a power switch for the electric heater and the motor.
FIG. 5 shows a conventional ice making means comprising an ice making tray 11 provided with a thermostat 12 and a heater 13, and an ice discharging motor 14 for an ice discharging mechanism provided with an ice discharging claw 15, a cam 16, a contact LS1 for the cam 16, a cam 17 and a contact LS2 for the cam 17, wherein ice 18 in the ice making tray 11 can be discharged by rotating the claw 15. Further, water is supplied from a water supply pipe 19 into the ice making tray 11 through an electromagnetic valve 20.
When the ice 18 of a predetermined quantity is discharged by the ice discharging mechanism and stored in an ice storing box 21, a sensor 22 detects the ice stored in the ice storing box 21 to stop the power supply from a power source 23 so as to stop temporarily the ice making operation.
When the amount of the ice in the ice storing box 21 is reduced, the power is supplied from the power source 23 to start the ice making operation.
In a state shown in FIG. 5, the amount of the ice in the ice storing box 21 is reduced, the ice making operation is started, a predetermined quantity of water is supplied into the ice making tray 11, and the electromagnetic valve 20 is deenergized. In this state, the thermostat 12 is turned OFF, so that no power is applied to the heater 13 and the motor 14. When the water in the ice making tray 11 is frozen and the thermostat 12 is turned ON, the heater 13 and the motor 14 are energized, so that the ice 18 contacted with the ice making tray 11 is melted and discharged into the ice storing box 21 by the claw 15 rotated by the motor 14 in the ice discharging mechanism. The rotation of the motor 14 is continued, so that the contact LS1 is turned ON by the cam 16. As a result, the electromagnetic valve 20 is operated to start the water supply, a quantity of water corresponding to the angular position of the motor 14 is supplied, and the ice making operation is restarted. The above motions are repeated until the sensor 22 for sensing the ice stored in the ice storing box is turned OFF.
In the conventional automatic ice making apparatus thus far described, the setting temperature of the ice making tray for freezing water positively is set to a value lower than a value required actually to freeze water so as to have a large play in consideration of the fluctuation in temperature in a freezing chamber, in mounting condition of the temperature sensor or the like. Accordingly, the conventional apparatus has such a defect that an ice making time becomes long, because a long time is required until the temperature of the ice making tray is lowered more than the temperature at which the temperature sensor is operated.
This problem will now be explained detail.
FIG. 1 shows ice making operation steps, temperature variations of the ice making tray and freezing states of water in one cycle of ice making operations of a general automatic ice making apparatus. First of all, the temperature of the ice making tray is maintained at a constant value substantially between a state that water on the ice making tray is frozen partially and a state that the water is frozen perfectly, because the ice making tray absorbs the heat of condensation.
After the freezing of water is completed, the temperature is lowered, because no heat of condensation is generated. When the temperature sensor detects the freeze of water, the electric heater is energized to elevate the temperature of the ice making tray, so that the ice contacted with the ice making tray is melted, and the ice is discharged to finish one cycle of the ice making operation.
In order to reduce the ice making time in the conventional automatic ice making apparatus, the setting value of a freeze judging temperature is approached as near as possible to the actual freezing temperature. However, the output value of the temperature sensor for the ice making tray, which may be maintained constant substantially while the water is condensed is fluctuated according to the temperature in the freezing chamber and the mounting condition of the temperature sensor or the like. Accordingly, a play according to the fluctuation must be necessary in the temperature setting. This results in the time until the sensor judges the freeze of water becomes about twice a time required for freezing the water actually in the automatic ice making apparatus practically used.
As stated in the first example of the prior art, the energization of the heater is controlled by the thermostat and accordingly a play must be added in the setting temperature similar to the control of the heater, so that the electric power supplied to the heater after the ice has been removed from the tray actually becomes wasteful.
In said conventional automatic ice making apparatus, further, there is an inconvenience such as the water overflow due to the water supply of plural times, and an abnormal stopping etc. in each operation of the water supply, cooling and heating for removing ice from the ice making tray.
Further, the electric heater for removing the ice from the ice making tray is deenergized by using a temperature fuse when the electric heater is overheated. Accordingly, the repair of the fuse is necessary when the temperature fuse is cut.
Further, it is a general manner that a solenoid valve for supplying water is opened for a constant period of time so as to supply a constant amount of water.
Further, in the apparatus having a water level detecting function using a thermistor, the water level is detected by self heating the thermistor by passing an overcurrent therethrough, and detecting the reduction of the temperature of the thermistor when the thermistor is immersed into the water.
If the solenoid valve for supplying water is opened for a constant period of time as in the prior art, a constant amount of water can be supplied under the condition that the water pressure in the water pipe is constant. However, the amount of supply water is reduced and the resultant amount of ice becomes small, if the water pressure is reduced, the ability of the solenoid valve for supplying water is lowered, or a filter for filtering water is clogged.
In the extra case, such an inconvenience that the apparatus is operated without supplying water would be generated.
If a dedicated sensor is used for the water level detection, the cost becomes high. Further, in the general water level sensor using a thermistor, an overcurrent is passed through the thermistor to heat it, and the water level is detected by the reduction of the temperature of the thermistor when the thermistor is immersed into the water. Accordingly, a circuit for applying an overcurrent to the thermistor other than a circuit for reading the output of the sensor must be added, so that the cost becomes higher.
An automatic ice making apparatus according to the present invention is so constructed that a temperature and a temperature variation rate can be detected in sequence in an entire range of the temperature by using a sensor which can sense a temperature and a temperature variation rate of an ice making tray continueously and a detection circuit therefor.
According to the automatic ice making apparatus of the present invention, the freeze of water is judged by detecting not only a predetermined temperature but also the temperature variation rate, so that an influence of the fluctuation of the output value of the temperature sensor due to the temperature in the freezing chamber and the mounting condition of the temperature sensor can be reduced considerably. The judgement of freeze of water can be carried out by detecting a difference between the temperature variation rate in the course of freezing of water and the temperature variation rate after the freeze of water.
Further, a time between actual removing of ice and the deenergization of the heater can be shortened, so that the power comsumption can be reduced, because the precision of the judgement of the separation of ice is enhanced.
Further, in the automatic ice making apparatus according to the present invention, the temperature and the temperature variation rate of the ice making tray can be detected, so that the apparatus itself can recognize a current operation state in the operation steps shown in FIG. 1 or the abnormal state. For example, if the temperature is more than 0xc2x0 C. and the temperature variation rate is minus, the operation state is judged as in the water cooling state after the water supply. If the temperature is lower than 0xc2x0 C. and the temperature variation rate is zero, the operation state is judged as in the water freezing state. Accordingly, the actual operation state can be recognized and a suitable action can be carried out when the abnormal state is generated.
Further, an abnormal overheating state can be judged if the temperature is excessive, so that the operation of the apparatus can be stopped before the temperature fuse is cut.
Further, in the automatic ice making apparatus according to the present invention, a constant amount of water can always be supplied by using a control circuit for controlling the amount of water supply. Further, a water level detection sensor compatible with the temperature sensor for detecting the freeze of water can be used.
In the automatic ice making apparatus of the present invention, when the temperature variation of the ice making tray becomes a predetermined value, a water level of supplied water is determined as a required value by using a thermistor and a microprocessor including an A/D converter, so that a solenoid valve for supplying water is controlled.
No dedicating sensor for detecting the water level is added but the thermistor for detecting the freeze of water is therefor used.
Further, the elevation of the temperature is detected by the fact that the automatic ice making apparatus is installed in the freezing chamber, so that the thermistor of the cooled state is brought into contact with supplied water.
Other objects and features of the present invention will become apparent from the following description taking in connection with the accompanying drawings.